The labelling reagent [18F]2-fluoroethyl tosylate is a widely used building block for the radiosynthesis of a number of small molecules (Musachio, J. L., Shah, J. & Pike, V. W. Radiosyntheses and reactivities of novel [18F]2-fluoroethyl arylsulfonates. J. label. Comp. Radiophann. 48, 735-747 (2005)). This strategy is generally applied in cases where a one-step approach fails (i.e. the use of a leaving group at the substrate). For a successful alkylation step, it is important to obtain [18F]2-fluoroethyl tosylate in high specific radioactivity and/or chemical purity. Currently, product purification can be seen as a challenge in the radiosynthesis of [18F]2-fluoroethyl tosylate. The preferred literature methods are based either on preparative HPLC or hexane/diethylether SPE (Wadsak, W. et al. F-18 fluoroethylations: different strategies for the rapid translation of C-11-methylated radiotracers. Nucl. Med. & Biol. 34, 1019-1028 (2007)). The present invention described below provides a method of purifying [18F]-fluoroalkyl tosylates.